Elevators typically comprise a car and, optionally, a counterweight which may be displaced for example within an elevator shaft to different levels in order to transport persons or items for example to various floors within a building. In a common type of elevator, the car and/or the counterweight are supported by a suspension member arrangement comprising one or more suspension members. A suspension member may be a member which may carry heavy loads in a tension direction and which may be bent in a direction transverse to the tension direction. For example, a suspension member may be a rope or a belt. Typically, suspension members comprise a plurality of cords. The cords may be made for example with a metal such as steel.
During operation of the elevator, suspension members have to carry high loads and are typically repeatedly bent when running along for example a traction sheave, a deflection sheave or other types of sheaves. Accordingly, substantial stress is applied to the suspension member arrangement during operation.
However, as elevators may typically be used by people for transportation along very significant heights, very high security requirements have to be fulfilled. For example, it has to be safeguarded that the suspension member arrangement can always guarantee safe support of the car and/or the counterweight. For such purposes, safety regulations rule that any substantial deterioration of an initial load bearing capacity of a suspension member arrangement can be detected such that for example counter-measures such as replacing a faulty suspension member from the suspension member arrangement may be initiated.
Generally, a load bearing capacity of a suspension member may be specified when designing the suspension member and may then be physically tested upon completion of the fabrication of the suspension member. Physical tests may comprise for example tensile loading of the suspension member and measuring the suspension member's reaction to an application of high tensile forces.
However, during actual operation of the elevator, it may be difficult or even impossible to perform such physical tests. With conventional steel ropes serving as suspension members, visual checking of a rope condition has been possible. However, in modern suspension members, load bearing cords are typically enclosed in a coating or matrix and are therefore not visible from outside. Therefore, alternative approaches for determining a load bearing capacity in a suspension member arrangement or determining parameters related thereto have been developed.
For example, elevator load bearing member wear and failure detection has been described in EP 1 730 066 B1. A method and apparatus for detecting elevator rope degradation using electrical resistance is described in U.S. Pat. No. 7,123,030 B2. Electrical signal application strategies for monitoring a condition of an elevator load bearing member are described in US 2011/0284331 A1 and U.S. Pat. No. 8,424,653 B2. Electrical signal application strategies for monitoring a condition of an elevator load bearing member are described in US 2008/0223668 A1 and U.S. Pat. No. 8,011,479 B2. A simplified resistance based belt type suspension inspection is disclosed in US 2013/0207668 A1. An elevator system belt type suspension having connecting devices attached thereto is described in WO 2011/098847 A1. A method for detection of wear or failure in a load bearing member of an elevator is described in WO 2013/135285 A1. Electrical signal application strategies for monitoring a condition of an elevator load bearing member are described in EP 1 732 837 B1. “Health Monitoring for Coated Steel Belts in an Elevator System” have been described in a research article of Huaming Lei et al. in the Journal of Sensors, Volume 2012, Article ID 750261, 5 pages, doi: 10.1155/2012/750261.
There may be a need for an alternative method and device for detecting a deterioration state of a load bearing capacity in a suspension member arrangement for an elevator. Particularly, there may be a need for such method and device which enable fulfilling high safety requirements, simple implementation and/or low cost.